Method and apparatus for reporting power headroom information in mobile communication system supporting carrier aggregation

ABSTRACT

A method and apparatus for reporting Power Headroom (PH) of a User Equipment (UE) per carrier efficiently in a mobile communication system supporting carrier aggregation are provided. The method includes calculating PHs for multiple activated carriers based on whether data channel transmission takes place on each carrier, configuring indicators indicating whether the data channel transmission takes place on the corresponding carriers, and transmitting the PHs and indicators as aggregated in an extended PH Report (PHR) on one of the carriers.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit under 35 U.S.C. §119(e) of aprovisional patent application filed on Aug. 10, 2010 in the U.S. PatentOffice and assigned Ser. No. 61/372,452, of a provisional patentapplication filed on Aug. 16, 2010 in the U.S. Patent Office andassigned Ser. No. 61/374,160, of a provisional patent application filedon Sep. 16, 2010 in the U.S. Patent Office and assigned Ser. No.61/383,437, of a provisional patent application filed on Oct. 4, 2010 inthe U.S. Patent Office and assigned Ser. No. 61/389,476, of aprovisional patent application filed on Oct. 12, 2010 in the U.S. PatentOffice and assigned Ser. No. 61/392,436, and of a provisional patentapplication filed on Nov. 5, 2010 in the U.S. Patent Office and assignedSer. No. 61/410,493, and under 35 U.S.C. §119(a) of a Korean patentapplication filed on Jul. 26, 2011 in the Korean Intellectual PropertyOffice and assigned Serial No. 10-2011-0074084, the entire disclosuresof which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a mobile communication systemsupporting carrier aggregation. More specifically, the present inventionrelates to a method and apparatus for reporting Power Headroom (PH) of aUser Equipment (UE) per carrier efficiently in a mobile communicationsystem supporting carrier aggregation.

2. Description of the Related Art

Mobile communication systems developed to provide subscribers with voicecommunication services on the move. With the rapid advance oftechnology, mobile communication systems have evolved to support highspeed data communication services as well as standard voicecommunication services.

Recently, Long Term Evolution (LTE) is under development as the nextgeneration mobile communication system of the 3^(rd) GenerationPartnership Project (3GPP). The LTE system is a technology for realizinghigh-speed packet-based communication at about 100 Mbps. A discussion isbeing held on several schemes for LTE, including one scheme for reducingthe number of nodes located in a communication path by simplifying aconfiguration of the network, and another scheme for maximallyapproximating wireless protocols to wireless channels.

Unlike voice services, resources for data services are allocatedaccording to the data amount to be transmitted and channel condition.Accordingly, in a wireless communication system such as a cellularcommunication system, a scheduler manages resources according to theresource amount, channel condition, and data amount. This is also thecase in the LTE system, in which the scheduler located in the basestation manages and allocates the radio resource.

Recently, LTE-Advanced (LTE-A) is actively being discussed as anevolution of LTE with new techniques to increase data rates. Carrieraggregation is one of the representative techniques that are newlyadopted in LTE-A. Unlike the data communication of the related art inwhich a User Equipment (UE) uses a single uplink carrier and a singledownlink carrier, carrier aggregation enables the UE to use multipleuplink and/or downlink carriers. Since the uplink transmission powerdetermination algorithm is designed for the UE operating with one uplinkcarrier and one downlink carrier, it is difficult to apply thetransmission power determination process for uplink transmission powerdetermination of the UE supporting carrier aggregation. There is a needto define a procedure and method for reporting Power Headroom (PH) ofthe UE supporting carrier aggregation.

SUMMARY OF THE INVENTION

Aspects of the present invention are to address at least theabove-mentioned problems and/or disadvantages and to provide at leastthe advantages described below. Accordingly, an aspect of the presentinvention is to provide a method and apparatus for reporting PowerHeadroom (PH) of a UE efficiently in the mobile communication systemsupporting carrier aggregation. An aspect of the present invention is toprovide a mechanism for reporting per-carrier PHs in a Power HeadroomReport (PHR) transmitted on one of the multiple carriers.

In accordance with an aspect of the present invention, a method forreporting PH of a terminal in a mobile communication system supportingcarrier aggregation is provided. The method includes calculating PHs formultiple activated carriers based on whether data channel transmissiontakes place on each carrier, configuring indicators indicating whetherthe data channel transmission takes place on the corresponding carriers,and transmitting the PHs and indicators as aggregated in an extended PHRon one of the carriers.

In accordance with another aspect of the present invention, an apparatusfor reporting PH of a terminal in a mobile communication systemsupporting carrier aggregation is provided. The apparatus includes a PHcalculator for calculating PHs for multiple activated carriers based onwhether data channel transmission takes place on each carrier, acontroller for configuring indicators indicating whether the datachannel transmission takes place on the corresponding carriers and forgenerating an extended PHR with the PHs and the indicators, and atransceiver for transmitting the extended PHR on one of the carriers.

In accordance with another aspect of the present invention, a method fora base station to receive PH in a mobile communication system supportingcarrier aggregation is provided. The method includes receiving anextended PHR containing multiple PHs for multiple activated carriers andindicators corresponding to the PHs through one of the carriers, andchecking each PH to determine whether data channel transmission takesplace on the carrier corresponding to the PH.

In accordance with another aspect of the present invention, an apparatusfor a terminal to receive PH in a mobile communication system isprovided. The apparatus includes a transceiver for receiving an extendedPHR containing multiple PHs for multiple activated carriers andindicators corresponding to the PHs through one of the carriers, and acontroller for checking each PH to determine whether data channeltransmission takes place on the carrier corresponding to the PH.

According to another aspect of the present invention, a method forreporting PH of a terminal in a mobile communication system is provided.The method includes when a PHR is triggered for a carrier cell,determining whether a Physical Uplink Shared Channel (PUSCH) takes placein the carrier cell, calculating a PH for the carrier cell based onwhether the PUSCH takes place in the carrier cell, inserting thecalculated PH into a PHR, inserting an indicator into the PHR, theindicator indicating whether the PUSCH takes place in the carrier cell,and transmitting the PHR to a base station.

Other aspects, advantages, and salient features of the invention willbecome apparent to those skilled in the art from the following detaileddescription, which, taken in conjunction with the annexed drawings,discloses exemplary embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, features, and advantages of certainexemplary embodiments of the present invention will be more apparentfrom the following description taken in conjunction with theaccompanying drawings, in which:

FIG. 1 is a diagram illustrating an architecture of a mobilecommunication system according to an exemplary embodiment of the presentinvention;

FIG. 2 is a diagram illustrating a protocol stack of a mobilecommunication system according to an exemplary embodiment of the presentinvention;

FIG. 3 is a diagram illustrating an exemplary situation of carrieraggregation in a mobile communication system according to an exemplaryembodiment of the present invention;

FIG. 4 is a conceptual diagram illustrating a principle of carrieraggregation for use in a mobile communication according to an exemplaryembodiment of the present invention;

FIG. 5 is a diagram illustrating an exemplary scenario of Power Headroom(PH) reporting according to an exemplary embodiment of the presentinvention;

FIG. 6 is a flowchart illustrating a PH reporting procedure of a UserEquipment (UE) according to an exemplary embodiment of the presentinvention;

FIG. 7 is a flowchart illustrating a PH reception procedure of anevolved Node B (eNB) according to an exemplary embodiment of the presentinvention; and

FIG. 8 is a block diagram illustrating a configuration of a PH reportingapparatus of the UE according to an exemplary embodiment of the presentinvention.

Throughout the drawings, it should be noted that like reference numbersare used to depict the same or similar elements, features, andstructures.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

The following description with reference to the accompanying drawings isprovided to assist in a comprehensive understanding of exemplaryembodiments of the invention as defined by the claims and theirequivalents. It includes various specific details to assist in thatunderstanding, but these are to be regarded as merely exemplary.Accordingly, those of ordinary skill in the art will recognize thatvarious changes and modifications of the embodiments described hereincan be made without departing from the scope and spirit of theinvention. In addition, descriptions of well-known functions andconstructions may be omitted for clarity and conciseness.

The terms and words used in the following description and claims are notlimited to the bibliographical meanings, but are merely used by theinventor to enable a clear and consistent understanding of theinvention. Accordingly, it should be apparent to those skilled in theart that the following description of exemplary embodiments of thepresent invention is provided for illustration purposes only and not forthe purpose of limiting the invention as defined by the appended claimsand their equivalents.

It is to be understood that the singular forms “a,” “an,” and “the”include plural referents unless the context clearly dictates otherwise.Thus, for example, reference to “a component surface” includes referenceto one or more of such surfaces.

Exemplary embodiments of the present invention relate to a method andapparatus for a User Equipment (UE) to report Power Headroom (PH)information efficiently in the mobile communication system supportingcarrier aggregation. An exemplary mobile communication system to whichan exemplary embodiment of the present invention is applied is describedbelow with reference to FIGS. 1 to 3. The description is directed to aLong Term Evolution (LTE) system, but other wireless communicationtechnologies may also be employed.

FIG. 1 is a diagram illustrating an architecture of a mobilecommunication system according to an exemplary embodiment of the presentinvention.

Referring to FIG. 1, the radio access network of the mobilecommunication system includes evolved Node Bs (eNBs) 105, 110, 115, and120, a Mobility Management Entity (MME) 125, and a Serving-Gateway(S-GW) 130. The UE 135 connects to an external network via eNBs 105,110, 115, and 120 and the S-GW 130.

The eNBs 105, 110, 115, and 120 correspond to legacy node Bs ofUniversal Mobile Communications System (UMTS). The eNBs 105, 110, 115,and 120 allow the UE establish a radio link and are responsible forcomplicated functions as compared to the legacy node B. In the LTEsystem, all user traffic, including real time services such as Voiceover Internet Protocol (VoIP), is provided through a shared channel andthus there is a need of a device which is located in the eNB to scheduledata based on the state information of the UEs. In order to implement adata rate of up to 100 Mbps, the LTE system adopts Orthogonal FrequencyDivision Multiplexing (OFDM) as a radio access technology. The LTEsystem adopts Adaptive Modulation and Coding (AMC) to determine themodulation scheme and channel coding rate according to the channelcondition of the UE.

S-GW 130 is an entity to provide data bearers so as to establish andrelease data bearers under the control of the MME 125. MME 125 isresponsible for various control functions and is connected to the eNBs105, 110, 115, and 120.

FIG. 2 is a diagram illustrating a protocol stack of the mobilecommunication system according to an exemplary embodiment of the presentinvention.

Referring to FIG. 2, the protocol stack of the LTE system includesPacket Data Convergence Protocol (PDCP) layer 205 and 240, Radio LinkControl (RLC) layer 210 and 235, Medium Access Control (MAC) layer 215and 230, and Physical (PHY) layer 220 and 225. The PDCP layer 205 and240 is responsible for Internet Protocol (IP) headercompression/decompression. The RLC layer 210 and 235 is responsible forsegmenting the PDCP Protocol Data Unit (PDU) into segments in a sizeappropriate for Automatic Repeat Request (ARQ) operation. The MAC layer215 and 230 is responsible for establishing connections to a pluralityof RLC entities so as to multiplex the RLC PDUs into MAC PDUs anddemultiplex the MAC PDUs into RLC PDUs. The PHY layer 220 and 225performs channel coding on the MAC PDU and modulates the MAC PDU intoOFDM symbols to transmit over a radio channel, or performs demodulatingand channel-decoding on the received OFDM symbols and delivers thedecoded data to a higher layer. The data input to a protocol entity isreferred to as Service Data Unit (SDU), and the data output by theprotocol entity is referred to as a PDU.

FIG. 3 is a diagram illustrating an exemplary situation of carrieraggregation in the mobile communication system according to an exemplaryembodiment of the present invention.

Referring to FIG. 3, an eNB typically uses multiple carriers transmittedand received in different frequency bands. For example, the eNB 305 maybe configured to use the carrier 315 with center frequency f1 and thecarrier 310 with center frequency f3. If carrier aggregation is notsupported, the UE 330 transmits/receives data using just one of thecarriers 310 and 315. However, the UE 330 having the carrier aggregationcapability may transmit/receive data using both the carriers 310 and315.

The eNB may increase the amount of resources to be allocated to the UEhaving the carrier aggregation capability according to the channelcondition of the UE so as to improve the data rate of the UE. If a cellis configured with one downlink carrier and one uplink carrier, thecarrier aggregation can be understood as if the UE communicates data viamultiple cells. With the use of carrier aggregation, the maximum datarate increases in proportion to the number of aggregated carriers. Theaggregated carriers are configured via Radio Resource Control (RRC)signaling. In LTE, it is possible to add or remove a carrier to or fromthe carrier aggregation using an RRCConnectionReconfiguration message.Although a specific carrier is configured, data transmission is notperformed yet. In order to use the corresponding carrier, the carrier isactivated by MAC signaling. In LTE, the configured carrier is activatedby a MAC Control Element (CE) in the MAC PDU. Since the service isprovided through the multiple activated carriers, multiple serving cellsmay exist.

In order to mitigate interference, the uplink transmission power may bemaintained below an appropriate level. For this purpose, the UEcalculates the uplink transmission power using a predetermined functionand performs uplink transmission at the calculated uplink transmissionpower. For example, the UE calculates the required uplink transmissionpower value by inputting the input values such as the schedulinginformation including resource amount and Modulation and Coding Scheme(MCS) allocated to the UE and information necessary for estimating thechannel condition such as path loss, and performs uplink transmission byapplying the calculated uplink transmission power value. The availableuplink transmission power value of the UE is limited to the maximumtransmission power value of the UE such that when the calculatedtransmission power value exceeds the maximum transmission power value,the UE performs the uplink transmission at the maximum transmissionpower. In this case, the uplink transmission power is not enough,resulting in uplink transmission quality degradation. Accordingly, theeNB may perform scheduling such that the required transmission powerdoes not exceed the maximum transmission power. However, since a fewparameters such as path loss cannot be determined by the eNB, the UEreports its PH value to the eNB by means of a PHR.

Several factors influence PH, including 1) allocated transmissionresource amount, 2) MCS to be applied to uplink transmission, 3) PathLoss (PL) of the related downlink carrier, and 4) accumulated value oftransmission power control command. The Path Loss and accumulatedtransmission power control command value are variable according to theuplink carrier such that, when multiple uplink carriers are aggregated,the transmission of the PHR may be configured per carrier. In order totransmit the PHR efficiently, it can be advantageous to report the PHsof all the uplink carriers on one uplink carrier. Depending on themanagement policy, it may be necessary to transmit the PH of the carrieron which no Physical Uplink Shared Channel (PUSCH) transmission actuallytakes place. In this case, it may be more efficient to report the PHs ofthe multiple uplink carriers on a single uplink carrier. For thispurpose, it is necessary to extend the PHR. The multiple PHs to becontained in a PHR can be arranged in a predetermined order.

FIG. 4 is a conceptual diagram illustrating a principle of carrieraggregation for use in the mobile communication according to anexemplary embodiment of the present invention.

Referring to FIG. 4, 5 uplink carriers can be aggregated for the UE, andone of the aggregated carriers can be selected to transmit the PHs forthe 5 uplink carriers. For example, when three uplink carriers 440, 445,and 450 are aggregated for the UE, a PHR can be configured to carry thePHs for the three uplink carriers.

A PHR is triggered when the path loss of the connected downlink carrieris equal to or greater than a predetermined threshold value, a prohibitPHR time expires, or a predetermined time period elapses after the lastPHR generation. Once PHR has triggered, the UE waits until the timeavailable for the uplink transmission arrives, e.g., the time for whichthe uplink transmission resource is allocated, rather than transmit thePHR immediately. This is because PHR is not time-sensitive information.The UE transmits PHR at the first uplink transmission. PHR is the MAClayer control information and has the length of 8 bits. The first twobits of PHR are reserved for future use, and the remaining 6 bits areused to indicate the value in the range between −23 dB and 40 dB as thepower headroom of the UE. The UE calculates the PH using the followingEquation 1:PH(i)=P _(CMAX,c)(i)−{10 log₁₀(M _(PUSCH,c)(i))+P _(O) _(_)_(PUSCH,c)(j)+α_(c)(j)·PL_(c)+Δ_(TF,c)(i)+f _(c)(i)}  1

The PH(i) of the i^(th) subframe in the serving cell c is calculatedwith the maximum uplink transmission power P_(CMAX,c)(i), number ofresource blocks M_(PUSCH,c)(i), power offset derived from MCS Δ_(TF,c),Path Loss PL_(c), and accumulated Transmission Power Control (TPC)commands f_(c)(i). In Equation 1, PL_(c) denotes the pass loss of a cellwhich provides the information on the path loss in the service cell c.The path loss used to determine uplink transmission power of a certainserving cell is the path loss of the downlink channel of thecorresponding cell or the path loss of a downlink channel of anothercell. The cell of which path loss is to be used is selected by the eNBand notified to the UE in the call setup process.

In Equation 1, f_(c)(i) is the accumulated value of the accumulated TPCcommands of the serving cell c. P_(O) _(_) _(PUSCH,C) denotes a higherlayer parameter corresponding to the sum of cell-specific andUE-specific values. Typically, P_(O) _(_) _(PUSCH,C) is set to a valuedetermined according to the transmission type of PUSCH, such as thesemi-persistent scheduling, dynamic scheduling, and random accessresponse. α_(c) denotes a 3-bit cell specific value provided from ahigher layer as the weight applied to the path loss when calculatinguplink transmission power (i.e., the higher this value, the more thepath loss influences the uplink transmission power), and its value islimited according to the transmission type of the PUSCH. j denotes thetransmission type of the PUSCH. The parameter j is set to 0 forsemi-persistent scheduling, 1 for dynamic scheduling, and 2 for randomaccess response. If there is no PUSCH transmission, M_(PUSCH) and Δ_(TF)are not applied to the Equation 1.

In a mobile communication system supporting carrier aggregation, therecan be a serving cell in which no PUSCH transmission takes place and aserving cell in which PUSCH transmission takes place. The PH for aserving cell may be reported in another serving cell. In the mobilecommunication system supporting carrier aggregation, when it isnecessary to report the PHs of multiple serving cells, the UE maytransmit the PHs in a single PHR. This method is advantageous to reducethe signaling overhead as compared to the method transmitting the PHsindividually, and the eNB can acquire the PH for the carrier on which noPUSCH is transmitted.

FIG. 5 is a diagram illustrating an exemplary scenario of PH reportingaccording to an exemplary embodiment of the present invention.

Referring to FIG. 5, a scenario is shown in which each of two servingcells CC1 and CC2 transmits the PHs of both the serving cells. In thetime duration 505 for which PUSCH transmission takes place in CC1 butnot in CC2, the UE can transmit MAC PDU 510 containing the CC1 PH 515and CC2 PH 520. In the time duration 525 for which PUSCH transmissiontakes place in CC2 but not in CC1, the UE can transmit MAC PDU 530containing the CC1 H 535 and CC2 PH 640.

Although no PUSCH is transmitted, the eNB may trigger PHR to acquire thepath loss information on a specific uplink carrier. Accordingly,exemplary embodiments of the present invention include a method forcalculating PH for the carrier carrying no PUSCH and a PHR format whichallows the eNB to identify the PH.

When PHR is triggered for a specific serving cell, the UE determines themethod for calculating the PH value according to whether the PUSCH istransmitted on the corresponding carrier. If PUSCH transmission takesplace in the corresponding serving cell, the PH is calculated usingEquation 1 as specified for a normal process. If no PUSCH transmissiontakes place in the corresponding serving cell, this means no resource isallocated for transmission such that the values of M_(PUSCH) and Δ_(TF)are apparent. Accordingly, there is a need of a device which allows theeNB and UE to calculate and interpret the PH using the same M_(PUSCH)and Δ_(TF). This goal can be addressed by defining a transmission format(transmission resource amount and MCS level) to be used for PHcalculation on the carrier carrying no PUSCH. Assuming one ResourceBlock (RB) and lowest MCS level as the reference transmission format,M_(PUSCH) and Δ_(TF) become 0 so as to be able to be omitted inEquation 1. Since no data transmission takes place in the correspondingserving cell, P_(CMAX,c)(i) does not exist. Accordingly, the value ofP_(CMAX,c)(i) should be determined. According to an exemplary embodimentof the present invention, a virtual P_(CMAX,c)(i) is defined and appliedfor such virtual transmission. P_(CMAX,c)(i) may be determined using themaximum allowed transmission power P_(EMAX) and the immanent maximumtransmission power of the UE P_(PowerClass). For example, P_(CMAX,c)(i)can be determined according to Equation 2.P _(CMAX,c)=min{P_(EMAX) ,P _(PowerClass)}  2

This has the same meaning that MPR, A-MPR, P-MPR, and T_(C) are all setto 0. P_(CMAX) is determined in the relationship of P_(CMAX) _(_)_(L)≦P_(CMAX)≦P_(CMAX) _(_) _(H). If all of MPR, A-MPR, P-MPR, and T_(C)are set to 0, P_(CMAX) _(_) _(L) becomes equal to P_(CMAX) _(_) _(H),resulting in P_(CMAX)=P_(CMAX) _(_) _(H). P_(CMAX) _(_) _(H) is the onehaving the least value among P_(PowerClass) and P_(EMAX). P_(EMAX) isthe cell-specific maximum allowed transmission power and P_(PowerClass)is the UE-specific Maximum allowed transmission power. Accordingly, whenno PUSCH transmission takes place in the serving cell, PH is defined byEquation 3:PH(i)=min{P_(EMAX) ,P _(PowerClass) }−{P _(O) _(_)_(PUSCH,c)(j)+α_(c)(j)·PL_(c) +f _(c)(i)}  3

In Equation 3, the values of the corresponding serving cells for whichPHs are calculated but not transmitted are determined with the P_(O)_(_) _(PUSCH,c), α_(c), f_(c)(i), PL_(C). The PH calculated by Equation3 is reported to the eNB along with other PHs transmitted in anotherserving cell. In view of eNB, it is possible to check the PHs formultiple serving cells with one PHR. One problem is that the eNB doesnot know whether each of the per-cell PHs contained in the PHR iscalculated according to PUSCH transmission and by using the PUSCHreference format according to an exemplary embodiment of the presentinvention. Without such information, the eNB may not be able tointerpret the reported PHs correctly, resulting in failure of efficientscheduling. In order to address this issue, an indicator for indicatingthe PUSCH transmission and use of the proposed PUSCH reference format isincluded in the PHR. The indicator is added for PH per activated servingcell. This indicator may be implemented with 1 bit. When calculating PHof a certain cell, if the PH is calculated under the assumption of PUSCHtransmission, i.e., using the actual transmission format, the UE setsthe corresponding bit to a predetermined value (e.g., 0). If PH iscalculated using the reference format (i.e., number of RBs=0 andΔ_(TF)=0), the UE sets the corresponding bit to a predetermined value(e.g., 1).

FIG. 6 is a flowchart illustrating a PH reporting procedure of a UEaccording to an exemplary embodiment of the present invention.

Referring to FIG. 6, the UE detects a PHR trigger for a specific servingcell in step 605. PHR can be triggered when the path loss of the linkeddownlink carrier becomes equal to or greater than a predetermined valueor periodically at a predetermined PHR period. Once the PHR trigger isdetected, the UE determines whether the real PUSCH transmission takesplace in the corresponding serving cell in step 610.

If the real PUSCH transmission takes place in the corresponding servingcell, the UE calculates PH according to a typical method in step 615.The UE calculates PH for the corresponding cell using Equation 1. The UEsets the PH type indicator so as to indicate that PH is calculatedaccording to the typical method in step 620. According to an exemplaryembodiment of the present invention, the PH type indicator is 1 bit andset to 0 for indicating the use of the normal PH method. Since PUSCHtransmission takes place in the corresponding serving cell, the UEplaces the calculated PH in the PHR to be transmitted in thecorresponding serving cell in step 640, and places the transmissionformat indicator indicating the use of real P_(CMAX) for thecorresponding PH in the PHR in step 645. Finally, the UE transmits thePHR in the corresponding cell in step 650. If necessary, the PH can betransmitted in another serving cell.

Otherwise, if no PUSCH transmission takes place in the correspondingserving cell, the UE calculates PH using the PH calculation equationaccording to an exemplary embodiment of the present invention in steps625 and 630. In step 625, P_(CMAX) is calculated with only the P_(EMAX)and P_(PowerClass) omitting the parameters related to real PUSCHtransmission. In step 630, PH is calculated with P_(CMAX) derived atstep 625 and reference transmission format excluding the parametersrelated to the real PUSCH transmission. After calculating PH, the UEsets the PH type indicator to 1 for the corresponding cell so as toindicate that the PH of the corresponding cell is derived based on thereference transmission format in step 635. If no PUSCH transmissiontakes place in the corresponding serving cell, this means that the PHRcannot be transmitted in the corresponding cell. Accordingly, the PH iscarried in the PHR transmitted in other cell of the eNB. Accordingly,the UE places the calculated PH in the PHR to be transmitted in theother serving cell at step 640. The UE places the transmission formatindicator indicating the use of virtual P_(CMAX) for the correspondingPH in the PHR in step 645. Finally, the UE transmits the PHR in theother serving cell.

According to an exemplary embodiment of the present invention, the UEreports the PHs for multiple carriers using an extended PHR in themobile communication system supporting carrier aggregation. The UEcalculates the PH for each of the activated carriers according towhether the real PUSCH transmission takes place thereon. If the realPUSCH transmission takes place, the UE calculates the PH usingEquation 1. If no PUSCH transmission takes place, the UE calculates thePH using Equation 3, i.e. using a predetermined reference format. The UEcalculates the PH under the assumption that the number of resourceblocks allocated in PUSCH M_(PUSCH) and the power offset Δ_(TF) are 0.The UE sets the transmission format indicators for indicating whetherthe real PUSCH transmissions take place in the corresponding cells. Ifthe PUSCH transmission takes place, the UE sets the transmission formatindicator to 0. If no PUSCH transmission takes place, the UE sets thetransmission format indicator to 1. The UE generates the extended PHRcontaining the PHs and indicators and transmits the extended PHR on oneof the carriers.

FIG. 7 is a flowchart illustrating a PH reception procedure of an eNBaccording to an exemplary embodiment of the present invention.

Referring to FIG. 7, the eNB receives a PHR from a UE in one of aplurality of serving cells in step 705. The PHR may include the PHs forthe current and other serving cells. The PH for the serving cell inwhich no PUSCH transmission takes place may be included in the PHR. Inorder to differentiate between the PHs for the serving cell in whichPUSCH transmission takes place and the serving cell in which no PUSCHtransmission takes place, the eNB checks the transmission formatindicators for individual PHs in step 710. If the transmission formatindicator is set to 0, the PH is calculated using the real P_(CMAX) forthe serving cell in which the real PUSCH transmission takes place. Ifthe transmission format indicator is set to 1, the PH is calculatedusing the virtual P_(CMAX) for the serving cell in which on PUSCHtransmission takes place. After checking the transmission formatindicator, the eNB determines whether the transmission format indicatoris set to 0 in step 715. If the transmission format indicator is set to0, the eNB determines that the PH is calculated with the real P_(CMAX)in step 720. This PH is used for scheduling the UE and channelestimation. If the transmission format indicator is set to 1, the eNBdetermines that the PH is calculated with the virtual P_(CMAX) in step725. This PH is used to predict the PL and estimate channel.

According to an exemplary embodiment of the present invention, if anextended PHR is received from a UE, the eNB uses the extended PHR todetermine uplink transmission power. The eNB includes a transceiver anda controller. The transceiver receives the extended PHR composed of thePHs for a plurality of carriers and indicators corresponding to the PHs,the extended PHR being transmitted on one of the plural activatedcarriers. The controller determines whether the PUSCH transmission takesplace on each of the carriers. If the transmission format indicator isset to 0, the controller determines that the PH is of the carrier onwhich PUSCH transmission takes place. If the PUSCH transmission takesplace on the carrier the PH is calculated using Equation 1. If thetransmission format indicator is set to 1, the controller determinesthat the PH is of the carrier on which no PUSCH transmission takesplace. If no PUSCH transmission takes place on the carrier, this meansthat the PH is calculated using Equation 3, i.e., calculated accordingto a predetermined reference format. In this manner, the controllerdetermines the uplink transmission powers for the respective carriersbased on the PHs according to whether PUSCH transmission takes place onthe respective carriers.

FIG. 8 is a block diagram illustrating a configuration of a PH reportingapparatus of the UE according to an exemplary embodiment of the presentinvention.

Referring to FIG. 8, the UE includes a transceiver 805, a PH calculator815, a controller 810, a multiplexer/demultiplexer 820, a controlmessage processor 835, and various higher layer devices 825 and 830. TheUE may include additional units (such as a display unit, input unit, andthe like) not shown here for purposes of clarity. Similarly, thefunctionality of two or more of the above units may be integrated into asingle component.

One or more of the units of the UE may be implemented as a softwarecomponent. Similarly, a unit may be implemented entirely as a hardware(such as one or more processors) or as a combination of hardware andsoftware components. However, it would be understood that at least someof the units would need to be implemented at least partially as ahardware components in order to carry out their function.

The transceiver 805 receives data and control signals on the downlinkcarriers and transmits data and control signals on the uplink carriers.When a plurality of carriers is aggregated, the transceiver 805 maytransmit/receive the data and control signals over a plurality ofcarriers.

The PH calculator 815 calculates PH according to the control signal fromthe controller 810 and sends the PH to the controller 810. When aplurality of carriers is aggregated, the PH calculator 815 can calculatePHs for the respective carriers. The PH calculator 815 calculates thePHs for the carriers according to whether PUSCH transmission takes placeon each carrier. If the PUSCH transmission takes place, the PHcalculator 815 calculates the PH according to a normal method. If noPUSCH transmission takes place, the PH calculator 815 calculates the PHwith a predetermined reference format. The PH calculator 815 derives thePH using a virtual P_(CMAX) for the carrier on which no PUSCHtransmission takes place according to an exemplary embodiment of thepresent invention.

The controller 810 controls the multiplexer/demultiplexer 820 togenerate MAC PDUs according to the control signal received by means ofthe transceiver 805, e.g. the scheduling information in the uplinkgrant. The controller detects the PHR trigger. If a PHR trigger isdetected, the controller 810 controls the PH calculator 815 to calculatethe PH. Whether PHR is triggered can be determined according to the PHRparameter provided by the control message processor 835. If the PHs ofmultiple uplink carriers are configured into a PHR, the controller 810controls the multiplexer/demultiplexer 820 to place in the MAC PDU anindicator indicating whether the PH for each carrier is derived fromreal P_(CMAX) or virtual P_(CMAX). The controller 810 generates the PHRwith the PHs provided by the PH calculator 815 and sends the PHR to themultiplexer/demultiplexer 820. If multiple carriers are aggregated, thecontroller 810 may report the PHs using an extended PHR configuredaccording to an exemplary embodiment of the present invention. Thecontroller 810 may configure the PHs of the multiple carriers into theextended PHR along with the transmission format indicators correspondingto the PHs. The controller 810 may transmit the extended PHR on one ofthe multiple carriers.

The multiplexer/demultiplexer 820 multiplexes the data from the higherlayer devices 825 and 830 and/or control message processor 835 anddemultiplexes the data received by the transceiver 805 to the higherlayer devices 825 and 830 and/or the control message processor 835.

The control message processor 835 processes the control messagetransmitted by the network and takes a necessary action. The controlmessage processor 835 forwards the PHR parameter carried in the controlmessage to the controller 810 or the information on the newly activatedcarriers to the transceiver 805 to set the carriers. The higher layerdevices 825 and 830 may be implemented for the respective services so asto deliver the data generated by the user service such as File TransferProtocol (FTP) and VoIP to the multiplexer/demultiplexer 820 or processand deliver the data form the multiplexer/demultiplexer 820 to theservice applications of the higher layer.

As described above, the PH reporting method and apparatus for a mobilecommunication system supporting carrier aggregation according toexemplary embodiments of the present invention enables efficientreporting or the PH per carrier. If multiple carriers are aggregated,the UE can configure the PHs for the multiple carriers into a PHR. Byusing the per-carrier PHs transmitted in aggregated manner, it ispossible to determine the uplink transmission power more efficiently inthe mobile communication system supporting carrier aggregation.

While the invention has been shown and described with reference tocertain exemplary embodiments thereof, it will be understood by thoseskilled in the art that various changes in form and details may be madetherein without departing from the spirit and scope of the invention asdefined by the appended claims and their equivalents.

What is claimed is:
 1. A method for reporting power headroom (PH) of aterminal in a mobile communication system supporting carrieraggregation, the method comprising: calculating PHs for multipleactivated carriers based on whether data channel transmission takesplace on each carrier; configuring indicators for the PHs, eachindicator indicating whether a corresponding PH is calculated based onthe data channel transmission taking place on a corresponding carrier;and transmitting the PHs and the indicators in an extended PH report(PHR) on one of the multiple activated carriers.
 2. The method of claim1, wherein the calculating of the PHs comprises calculating, a PH for afirst activated carrier according to a predetermined reference format,if no data channel transmission takes place on the first activatedcarrier.
 3. The method of claim 2, wherein the PH for the firstactivated carrier is calculated under an assumption that a number ofresource blocks and power offset are “0”.
 4. The method of claim 2,wherein the PH for the first activated carrier is calculated under anassumption that a value of addition maximum power reduction (A-MRP) is“0”.
 5. The method of claim 1, wherein the configuring of the indicatorscomprises: setting an indicator to “0” for the PH on a correspondingcarrier where the data channel transmission takes place; and setting anindicator to “1” for the PH on a corresponding carrier where no datachannel transmission takes place.
 6. An apparatus for reporting powerheadroom (PH) of a terminal in a mobile communication system supportingcarrier aggregation, the apparatus comprising: a transceiver configuredto transmit and receive a signal; and a controller configured to:calculate PHs for multiple activated carriers based on whether datachannel transmission takes place on each carrier, configure indicatorsfor the PHs, each indicator indicating whether a corresponding PH iscalculated based on the data channel transmission taking place on acorresponding carrier, and control to transmit the PHs and theindicators in an extended PH report (PHR) on one of the multipleactivated carriers.
 7. The apparatus of claim 6, wherein the controlleris configured to calculate a PH for a first activated carrier accordingto a predetermined reference format if no data channel transmissiontakes place on the first activated carrier.
 8. The apparatus of claim 7,wherein the PH for the first activated carrier is calculated under anassumption that a number of resource blocks and power offset are “0”. 9.The method of claim 7, wherein the PH for the first activated carrier iscalculated under an assumption that a value of addition maximum powerreduction (A-MRP) is “0”.
 10. The apparatus of claim 6, wherein thecontroller is configured to set an indicator to “0” for the PH on acorresponding carrier where the data channel transmission takes placeand to set an indicator to “1” for the PH on a corresponding carrierwhere no data channel transmission takes place.
 11. A method for a basestation to receive power headroom (PH) in a mobile communication systemsupporting carrier aggregation, the method comprising: receiving anextended PH report (PHR) including multiple PHs for multiple activatedcarriers and indicators corresponding to one of the PHs through one ofthe multiple activated carriers; and checking each PH to determinewhether data channel transmission takes place on the carriercorresponding to the PH.
 12. The method of claim 11, further comprisingdetermining that a PH for a first activated carrier is calculatedaccording to a predetermined reference format, if no data channeltransmission takes place on the first activated carrier.
 13. The methodof claim 12, wherein the determining that the PH for the first activatedcarrier is calculated according to the predetermined reference formatcomprises determining that the PH is calculated under an assumption thata number of resource blocks and power offset are “0”.
 14. The method ofclaim 12, wherein the determining that the PH for the first activatedcarrier is calculated according to the predetermined reference formatcomprises determining that the PH is calculated under an assumption thata value of addition maximum power reduction (A-MRP) is “0”.
 15. Themethod of claim 11, wherein an indicator is set to “0” for the PH on acorresponding carrier where the data channel transmission takes place,and an indicator is set to “1” for the PH on a corresponding carrierwhere no data channel transmission takes place.
 16. An apparatus for abase station to receive power headroom (PH) in a mobile communicationsystem, the apparatus comprising: a transceiver configured to transmitand to receive a signal; and a controller configured to: control toreceive an extended PH report (PHR) including multiple PHs for multipleactivated carriers and indicators corresponding to one of the PHsthrough one of the multiple activated carriers, and check each PH todetermine whether data channel transmission takes place on the carriercorresponding to the PH.
 17. The apparatus of claim 16, wherein thecontroller is configured to determine that a PH for a first activatedcarrier is calculated according to a predetermined reference format, ifno data channel transmission takes place on the first activated carrier.18. The apparatus of claim 17, wherein the controller is furtherconfigured to determine that the PH for the first activated carrier iscalculated under an assumption that a number of resource blocks andpower offset are “0”, if it is determined that the PH is calculatedaccording to the predetermined reference format.
 19. The apparatus ofclaim 17, wherein the controller is further configured to determine thatthe PH for the first activated carrier is calculated under an assumptionthat a value of addition maximum power reduction (A-MRP) is “0”, if itis determined that the PH is calculated according to the predeterminedreference format.
 20. The apparatus of claim 16, wherein an indicator isset to “0” for the PH on a corresponding carrier where the data channeltransmission takes place, and an indicator is set to “1” for the PH on acorresponding carrier where no data channel transmission takes place.